Caption: Hurricane. Computer artwork showing how a hurricane forms. Warm moist air rises from the ocean surface (yellow upward arrows). As it rises it cools and its water vapour condenses to form clouds. The rising air is replaced by more warm moist air from below, a cycle that creates winds (red arrows) circulating around a central point. Cooled dry air at the top of the system is sucked downwards through the centre (yellow downward arrows), forming a positive feedback loop that intensifies the strength of the winds.